1. Field of the Invention
This invention relates to the manufacture of parts, such as, for example, aircraft, boat and automobile panels, embodying resins and/or adhesive materials.
2. Description of the Prior Art
The curing and/or bonding of shaped composite parts comprising fibers such as graphite or Kevlar fibers impregnated with thermosetting resins or of thin metallic sections or laminas or metallic and resinous sections with thermosetting adhesive therebetween, is recognized as an effective method of manufacturing lightweight, high strength panels.
In curing composite parts, the materials are generally placed on a shaped tool or mold in an uncured and somewhat pliant state. A relatively high degree of temperature and pressure is then applied thereto to remove air, moisture and volatiles from the material during the forming and curing operation.
In bonding thin sections of metal and a composite material together, a thermosetting adhesive is applied between the sections and they are likewise placed on a shaped tool and subjected to a high degree of temperature and pressure to remove the volatile, etc., therefrom during the forming and curing operation.
The bonding of shaped parts is generally accomplished by covering the materials to be bonded with a porous breather mat or pad, mounting a vacuum bag thereover and sealing the edges of the bag to the tool. The assembly is then placed in an autoclave and heated and pressurized therein while vacuum is applied to the vacuum bag to withdraw the air, volatiles, etc. from the part being treated.
The breather pad is preferably formed of intertwined flexible fibers to permit the application of a uniform pressure on the part to force it against the tool in order for it to accurately conform to the contour of the tool and insure the uniform evacuation of gaseous components therefrom. Such breather pads can, for example, be formed of nylon material in the manner disclosed and claimed in my copending patent application, Ser. No. 07/894,949, filed Jun. 8, 1992 now U.S. Pat. No. 5,261,993.
Heretofore, vacuum has generally been applied to the interior of the aforesaid vacuum bag by a suitable vacuum pump or the like connected through a hose to a vacuum valve or connector attached to the bag and communicating through an opening in the bag with its interior. Although these valves are generally satisfactory, any resinous material sucked through such a valve, quick disconnect, and hose to the pump tends to concentrate around the entrance to the valve and quick disconnect and to build up therein, as well as on the inside of the remainder of the vacuum system, thus reducing the amount of vacuum and eventually closing off the passages in the valve, connector, hose, etc., requiring replacement of these parts. It can even clog the vacuum pump in some cases to disable the whole system.
Also, as pressure is applied to the vacuum bag, the vacuum valve is pressed down against the breather pad, which results in a very small and undesirable evacuation path. Moreover, if there is insufficient room on the tool the valve is sometimes placed on top of the part which causes an undesired imprint thereof to be transferred to the surface of the part through the breather pad.
Accordingly, a principle object of the present invention is to provide means for overcoming the above-noted problems.
Another object of the invention is to provide vacuum-conveying means for evacuating a vacuum bag of the above type without any build-up of resins, etc., therein to reduce the amount of vacuum applied to the bag or even disable the system.
Still another object of the invention is to provide an evacuating path which will prevent resins, etc., from being transferred from the part being cured to the vacuum system.
A further object of the invention is to provide vacuum-conveying means which can be repetitively used for a large number of successive curing operations.
Yet another object of the invention is to provide vacuum-conveying means which is inexpensive and readily replaceable.
According to the invention, vacuum-conveying means is provided comprising a flexible tube of any desired length having an inner tubular liner of porous fibrous material which is mounted at one end of the tube for direct contact with said porous breather pad. A vacuum connector is mounted in contact with the liner at the opposite end of the tube and is connected to a suitable vacuum source. As vacuum is applied, the various gases, along with any resins, removed from a part being cured are passed through the breather pad and liner, enabling such resins to be deposited throughout the length of the liner. The liner preferably has a relatively large cross sectional area and can thus accumulate a considerable amount of resin, or other effluent, along its length without adverse effect on the evacuation process.
The vacuum connector is removably supported by a frame part to prevent strain from being applied to the vacuum tube which might otherwise distort the vacuum bag or pull the tube from its connection to the vacuum bag. It also permits quick and ready removal thereof from the connected vacuum bag after each curing operation.